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Changing size (looming) as a stimulus to accommodation and vergence
L N McLin1, C M Schor, P B Kruger
1School of Aerospace Medicine, Radiation Sciences Division, Brooks AFB, TX 78235.
Vision Research
|January 1, 1988
Summary
Changing object size directly stimulates accommodation and indirectly influences vergence via the accommodative convergence/accommodation (AC/A) ratio. This finding clarifies visual system responses to looming stimuli.
Area of Science:
- Ophthalmology
- Neuroscience
- Visual Science
Background:
- Accommodation and vergence are crucial for clear and single binocular vision.
- The relationship between these two vergence systems is complex and not fully understood, especially concerning responses to changing size stimuli.
Purpose of the Study:
- To investigate the dynamic interplay between accommodation and vergence when exposed to looming visual stimuli.
- To compare the visual system's response to changing size with established accommodative convergence/accommodation (AC/A) and convergence accommodation/convergence (CA/A) ratios.
Main Methods:
- Dynamic responses of vergence and accommodation were recorded using a dual-Purkinje-image eyetracker and optometer during sinusoidal looming of a visual target.
- The AC/A and CA/A ratios were determined using separate stimuli inducing blur and disparity variations.
Main Results:
- The motor response to changing size (looming) more closely resembled the AC/A ratio than the CA/A ratio.
- Adding a changing size stimulus reduced phase lags in accommodation and vergence responses.
- The CA/A ratio increased when changing size was combined with changing disparity, while the AC/A ratio remained unchanged with changing blur.
Conclusions:
- Changing size (looming) appears to directly stimulate accommodation.
- Vergence is secondarily stimulated by accommodation through an AC/A crosslink.
- These findings provide insights into the neural pathways governing vergence and accommodation control.